Wireless digital networks, such as networks operating under the current Electrical and Electronics Engineers (IEEE) 802.11 standards, are spreading in their popularity and availability. With such popularity, however, problems related to fast roaming tend to occur during high speed movement of a client device in a wireless network.
When a client device moves at a low speed in the wireless network, the client device can iteratively scan through a plurality of wireless channels and determine which network device to associate with. Specifically, the client device can send a request message, such as a probe request, and receive a response message, such as a probe response, from a network device in the neighborhood. Because the speed of client movement is rather slow, the change in location among multiple iterations typically does not cause the signal strength level (e.g., received signal strength indication, RSSI) to vary drastically, and thereby will not likely affect the accuracy of the scanning procedure.
Nevertheless, when a client device moves at a high speed in the wireless network, the change in location among multiple iterations of scanning can be so large that it causes the signal strength level (e.g., RSSI) to vary drastically, and thereby affects the accuracy of scanning. Hence, in order to ensure the accuracy of scanning when a client device moves at a high speed, the client device needs to reduce the scanning intervals. As a result, the client device will spend less time on data transmissions and more time on network device discovery when moving at a fast speed. Thus, network traffic could suffer apparent degradation and/or fluctuation.
Conventionally, a network device can maintain a list of adjacent network devices and the wireless channels that they communication on, and send the list to a client device when the client device needs to roam at a high speed. Thus, the client device uses the adjacent network device list it received from the network device that it currently is associated with to reduce the number of channels the client device needs to scan. However, because the adjacent network device list may not be up-to-date or complete, the conventional solution to channel scanning during fast roaming may not produce accurate results.
Moreover, the solution does not benefit much in a high density deployment of wireless network devices.